1. Field of the Invention
The present invention relates to a spread-spectrum based cellular mobile radio system comprising at least two radio base stations covering radio zones, and a plurality of mobile radio stations. The applied spread-spectrum technique can be a so-called direct sequence spread spectrum technique or a so-called frequency hopping spread spectrum technique, or the like.
The present invention further relates to a control arrangement, a radio base station, and a mobile radio station for use in such a system.
2. Discussion of the Related Art
A spread-spectrum based cellular mobile radio system of the above kind is known from the International Patent Application WO 91/07037, which discloses a CDMA (Code Division Multiple Access) spread-spectrum cellular mobile telephony system. Disclosed is a CDMA system with an overall power control so as combat the so-called near-far problem and thus to maximize the system capacity in terms of the number of simultaneous telephone calls that may be handled in a given system bandwidth. In general terms, the disclosed system tries to achieve in real-time that under fading conditions, all signals received in a radio base station from mobile radio stations arrive at the radio base station with equal field strength. It is thus avoided that otherwise weak signals are not overshadowed by much stronger signals arriving at the radio base station. Such weak signals would then not or hardly not be detectable. In WO 91/07037, with an overall real-time power control, it is attempted to realize favourable interference conditions. A CDMA mobile radio system is also disclosed in a patent application filed by the present applicant, namely European application No. 94 200 479.7, filed Feb. 25, 1994, due to a more sophisticated demodulation, the latter system being less prone to the so-called near-far problem the patent application WO 91/07037 is aiming to combat. Although the known systems achieve an increase in system capacity as compared to other CDMA systems, these systems do not allow for a more sophisticated control such as a controlled access of mobile radio stations to radio zones under interference conditions.